A phase change material (PCM) is a substance with a high heat of fusion that melts or solidifies at a specific temperature and that absorbs or releases heat during a change of phase (i.e., state of matter). PCM were first discovered in the 1950s and were extensively researched and put to practical use in the 1970s. Today, PCM have found application in construction materials, textiles, beddings, aerospace materials, and refrigeration equipment, to name only a few.
More than 6000 PCMs are currently known. They can be divided by material property into four major types: inorganic (e.g., salt hydrates), organic (e.g., paraffin, fatty acids, and their polymers), polymeric, and composite. Generally speaking, a PCM is made into “microcapsules” when used in mattresses. A “microcapsule” in this context refers to a tiny capsule formed by a process called microencapsulation to enclose a solid, liquid, or gaseous PCM (referred to as “core”) in a shell (referred to as “wall”), wherein the microencapsulation process is nowadays a rapidly developing, versatile, and fairly mature technique. Depending on product requirements, a PCM microcapsule may range from 0.01 μm to 1000 μm in size and have a spherical, granular, lumpy, or other shape.
To make a PCM mattress, PCM microcapsules are mixed into a foaming material, which is then formed into a mattress, or a finished mattress is coated with PCM microcapsules on the surface only. In either case, the “microcapsules” are used to absorb external heat, and theoretically a mattress possessing the properties of a PCM will be able to dissipate heat rapidly, allowing a user to lie comfortably on the mattress without having to resort to electrical appliances (e.g., an air conditioner that produces cool or warm air) for temperature regulation. However, the inventor of the present invention has found that either approach leaves something to be desired. “Mixing PCM microcapsules into a foaming material” is disadvantageous in that the PCM microcapsules tend to impair the elasticity and smoothness, and thus lower the quality, of the resulting mattress as early as when the PCM microcapsules are mixed with the foaming material to form the mattress. “Coating a mattress with PCM microcapsules”, on the other hand, produces a mattress which may lose its heat dissipation function when the body skin of a user lying on the mattress is pressed against and covers the PCM microcapsules. This is because the surface of the mattress will be covered by the user's body skin on one side and the foam in the mattress on the other side, making it impossible for any accumulated heat to escape. The PCM microcapsules may thus absorb too much heat to transfer to the ambient air effectively and hence fail to produce the intended cooling effect.
In light of the above, the inventor of the present invention wondered whether a novel structure with PCM microcapsules can be designed to have consistently high product yield and quality and to also solve the problem of heat accumulation resulting from a user's body skin covering the PCM microcapsules. The issue to be addressed by the present invention, therefore, is to improve the structures and manufacturing processes of various conventional mats according to the properties of PCM microcapsules so that the foregoing objective can be achieved.